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# `useScratch`
React sensor hook that tracks state of mouse "scrubs" (or "scratches").
## Usage
```jsx
import useScratch from 'react-use/lib/useScratch';
const Demo = () => {
const [ref, state] = useScratch();
const blockStyle: React.CSSProperties = {
position: 'relative',
width: 400,
height: 400,
border: '1px solid tomato',
};
const preStyle: React.CSSProperties = {
pointerEvents: 'none',
userSelect: 'none',
};
let { x = 0, y = 0, dx = 0, dy = 0 } = state;
if (dx < 0) [x, dx] = [x + dx, -dx];
if (dy < 0) [y, dy] = [y + dy, -dy];
const rectangleStyle: React.CSSProperties = {
position: 'absolute',
left: x,
top: y,
width: dx,
height: dy,
border: '1px solid tomato',
pointerEvents: 'none',
userSelect: 'none',
};
return (
<div ref={ref} style={blockStyle}>
<pre style={preStyle}>{JSON.stringify(state, null, 4)}</pre>
{state.isScratching && <div style={rectangleStyle} />}
</div>
);
};
```
## Reference
```ts
const [ref, state] = useScratch();
```
`state` is:
```ts
export interface ScratchSensorState {
isScratching: boolean;
start?: number;
end?: number;
x?: number;
y?: number;
dx?: number;
dy?: number;
docX?: number;
docY?: number;
posX?: number;
posY?: number;
elH?: number;
elW?: number;
elX?: number;
elY?: number;
}
```
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